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Proline X PO 12-S DFW XLT sealed down-fire wide enclosure for the PowerBass XL-1240T, 41 inches wide by 5.3125 inches tall, feet add 1.75 inches of height.
Proline X PO 12-S DFW XLT sealed down-fire wide enclosure, end panel with side-mounted terminal cup, 5.3125 inches tall by 14 inches deep.

Performance Optimized · Datasheet

Performance Optimized Down Fire Wide Sealed 12" Enclosure PowerBass XL-1240T · Single 12" Sealed enclosure

Net volume
0.720 cu ft after the brace and 0.126 cu ft displacement
Max mounting depth
3.8 in required, shallow mount
External dimensions
41 in W × 5.3125 in in the down fire position H × 14 in D
Front baffle
1.5 in double baffle, outer layer machined as a flush recess
Buy at Audio IntensityFactory-direct, ships from Tullahoma
PowerBass XL-1240TBuy at Audio Intensity
  • Alignment: 0.720 cu ft net. Qtc 0.923, Fc 57.9 Hz, F3 47.4 Hz
  • Down Fire Wide: 41"W x 14"D x 5.3125"H in down fire position, excludes standoffs, square corners
  • Versus the standard 24.89 x 15: 5.3 in tall and 0.40 cu ft net there, 5.3125 in tall and 0.720 cu ft net here
  • Driver: PowerBass XL-1240T, 400 W RMS, 7.5 mm Xmax, 3.8 in mounting depth, single 4 ohm, rear vented motor
  • Standoffs: Included, 1.75 in, shipped uninstalled. Installed height 7.0625 in

Spec of record

Technical specifications

SpecificationValue
SeriesProline X Performance Optimized Down Fire Wide
Compatible DriverPowerBass XL-1240T. Direct fit
Enclosure TypeSealed, down fire, floor coupled
Intended FitmentSpaces where height or depth is the limit and 41 in of run is available
Chamber ConfigurationSingle chamber, windowed U-brace, one side-mounted terminal cup
External Width41 in
External Depth14 in
External Height5.3125 in in the down fire position, excludes standoffs
Installed Height7.0625 in including the 1.75 in standoffs
Internal Volume, Gross0.85 cu ft
Internal Volume, Net0.720 cu ft after the brace and 0.126 cu ft displacement
Height Set ByDriver clearance: 0.75 in above the 3.8 in motor
AlignmentQtc 0.923, Fc 57.9 Hz, F3 47.4 Hz anechoic
Comparison, Standard 24.89 x 155.3 in tall, 0.40 cu ft net. Wide format is 5.3125 in tall with 0.720 cu ft net
Woofer Opening11.06 in (281 mm, PowerBass template; labelled 11 in)
Driver Mounting Depth3.8 in required, shallow mount
Driver MotorRear vented, pole vent may be fully obstructed
Driver Fs / Qts / Vas33 Hz / 0.526 / 42.37 L
Driver Displacement0.126 cu ft
PowerBass Published Target0.40 optimum, 0.30 to 0.85 acceptable. Their figures are GROSS and include driver displacement
Driver Power Handling400 W RMS, 800 W peak
Driver Voice CoilSingle 4 ohm, 2 in
Wiring4 ohms, no wiring choice
MaterialLangboard Elite 3/4 in MDF
ConstructionShopSabre CNC, V-groove and dado joinery
Panel Thickness0.75 in
Front Baffle1.5 in double baffle, outer layer machined as a flush recess
Internal BracingWindowed U-brace, dadoed to the shell
Corner ProfileSquare, Down Fire series standard
Driver MountingThreaded inserts with stainless machine screws
Terminal CupOne Proline X ABS and carbon fiber composite, side mounted, pre-wired 12 gauge OFC
StandoffsIncluded, 1.75 in, shipped uninstalled
DampingLight polyfill wall lining, does not alter acoustic volume
CarpetPlush Black
Bundle OptionsEnclosure only, bring your own PowerBass XL-1240T
Warranty1 Year Limited
Built InTullahoma, Tennessee

Modelled response

Performance in this enclosure

Net airspace
0.720
cu ft per chamber
System Qtc
0.92
sealed
Half power
47.4
Hz · F3
Xmax at
241
W RMS · no filter
With 25 Hz subsonic
247
W RMS · +3%
Amplifier
400
W RMS recommended
This enclosure holds 0.720 cu ft net per chamber. In it the PowerBass XL-1240T runs a system Qtc of 0.92 with half power at 47.4 Hz, and the cone reaches its 7.5 mm travel limit at 241 W, below the driver’s 400 W thermal rating, so travel is what stops you here, not heat. A 25 Hz subsonic filter adds little here: 247 W against 241 W, 3 percent. The box already resonates at 58 Hz, so its own rolloff has removed most of what the filter would have stopped.

01Is it a sealed driver?

Efficiency bandwidth product places the motor before anything else is decided.

EBP = Fs ÷ Qes = 55.3
SEALED 0–50 TRANSITION 50–100 PORTED 100–150 0 50 100 150 XL-1240T 55.3
XL-1240T · EBP 55.3
At 55.3 the XL-1240T sits in the transition band, not the sealed band. That is not a mismatch: a transition motor works in either alignment, and sealed buys a smaller box and a gentler roll-off at the cost of some low-end output. Stage 02 shows what this airspace actually does with it.

02What the box does to it

0.720 cu ft against a 42.4 L Vas.

α = Vas ÷ Vb = 2.08  ·  Fc = Fs√(α+1) = 58 Hz  ·  Qtc = 0.92
20 30 50 70 100 150 200 +6 +0 -6 -12 -18 -24 FREQUENCY · Hz LEVEL · dB −3 dB
XL-1240T · Qtc 0.92, Fc 58 Hz, F3 47.4 Hz
The box lifts resonance from 33.0 Hz free-air to 58 Hz and half power lands at 47.4 Hz, anechoic, before any cabin gain.

03The watts that reach Xmax (in this enclosure)

Travel scales with the square root of power, so there is one wattage that puts the cone exactly on 7.5 mm, and in this alignment a subsonic filter barely moves it.

PXmax = 241 W unfiltered  →  247 W with a 25 Hz subsonic
20 30 50 70 100 150 200 0 4 8 FREQUENCY · Hz CONE TRAVEL · mm PAST LINEAR TRAVEL · Xmax 7.5 mm 241 W reaches Xmax here
XL-1240T · 241 W, no filterXL-1240T · 247 W with subsonic at 25 Hz, 24 dB/octXmax 7.5 mm one-way
Every trace touches the limit and no further, because each is drawn at the exact power that puts that coil on 7.5 mm. Unfiltered that is 241 W, reached first at 37 Hz. It sits under the 400 W the driver can take thermally, so the enclosure sets the ceiling, not the voice coil. The dashed traces are the same driver behind a subsonic filter at 25 Hz, 24 dB/oct, and they sit almost on top of the solid ones: 247 W against 241 W. At 58 Hz the filter sits well below resonance, where the sealed alignment has already rolled the cone off at 12 dB/oct, so there is little wasted travel left for it to recover. Set it anyway to keep road rumble out of the cone, but do not size the amplifier around it.
ParamValueUnitNote
Fs33.00Hzfree-air resonance
Qts0.526XL-1240T
Vas42.37Lequivalent compliance
Sd510.7cm²effective piston area
Xmax7.5mmone-way linear travel
Pe400Wcontinuous RMS
SPL85.9dB1 W / 1 m, derived from T/S

Driver parameters as published by powerbassusa.com. Curves computed against this enclosure’s actual net airspace.

From the shop floor

Installer's take

Same XL-1240T as the standard 24.89 by 15 box, laid out 41 by 14. One inch shallower, 16.11 inches longer, and the same height to within a fraction, 5.3125 against 5.3, because the motor sets both. Measure all three dimensions before choosing between them.

Height here is set by the 3.8 inch motor, not the airspace: 0.75 inch above the motor is the floor, and at 41 by 14 that already buys 0.720 cubic feet net against the 0.40 the standard box was built to. That is a clearance fact, not a tuning target. More air lowers Qtc, which is the safe direction.

Alignment is Qtc 0.923 with F3 at 47.4 Hz.

Rear vented motor, so the pole vent can be blocked. PowerBass quotes 0.40 gross; this one is well over that and still inside their acceptable range. Single 4 ohm coil, nothing to get wrong.

Before you order

Questions

Why is this cabinet 41 inches wide instead of 24.89?

Because it trades length for depth and height. The standard single Down Fire platform is 24.89 wide by 15 deep; this one is 14 deep, 1 inch shallower, and runs 41 inches long to put the airspace along the length instead.

On this driver the motor sets the minimum height of both boxes, so it stands 5.3125 inches against 5.3 and the extra length becomes extra airspace. A 12 inch frame needs about 13 inches of baffle, so 14 is as shallow as a 12 can go.

How does this compare to the standard 24.89 x 15 XL-1240T enclosure?

The standard box is 24.89 by 15 by 5.3 inches and holds 0.40 cubic feet net. This one is 41 by 14 by 5.3125 inches and holds 0.720 cubic feet net.

Here the wide box holds more air because its height is set by motor clearance, not by an airspace target. More air lowers Qtc, the safe direction. Choose the standard box when length is limited, this one when depth is the limit and you have 41 inches of run.

What alignment does this enclosure produce?

At 0.720 cubic feet net the result is Qtc 0.923, Fc 57.9 Hz and F3 47.4 Hz, calculated from the driver's own published Thiele-Small parameters.

That is above the 0.707 maximally flat reference, so there is real lift near the corner rather than a textbook flat curve. The figures are anechoic; in a car, cabin gain adds real output below 50 Hz, so in-vehicle response runs deeper.

How much power should I run, and how do I wire it?

The XL-1240T is a single 4 ohm voice coil, so it presents 4 ohms and there is no wiring decision to make. Target 400 watts RMS and set gains properly rather than to a number.

How tall is this once the standoffs are on?

The cabinet is 5.3125 inches tall measured in the down fire position, excluding standoffs. The standoffs hold 1.75 inches under the baffle, so plan your space around 7.0625 inches installed.

The standoffs ship uninstalled, so you can place them to suit your floor, or leave them off and run the cabinet front firing or up firing.

Where is the terminal cup located on a down fire enclosure?

Side mounted. Every Proline X Performance Optimized enclosure uses a side mounted terminal cup regardless of alignment, whether standard, wedge, or down fire. On this cabinet that keeps the connection accessible with the enclosure installed, since the baffle faces the floor. The cup is our Proline X ABS and carbon fiber composite unit with stainless hardware, copper ring terminals, and pre-wired 12 gauge OFC.

How is this enclosure built?

V-groove and dado joinery, CNC cut on ShopSabre routers from Langboard Elite MDF, with square corners as the Down Fire standard. Every panel joint is a machined interlocking groove that locks before adhesive is applied, which keeps the cabinet airtight under sustained pressure cycling.

The 1.5 inch double baffle has its outer layer machined as a flush recess so the driver bolts to the inner layer, and a windowed U-brace stiffens the long panels. Polyfill is installed as a light wall lining; do not add more, since packing a sealed box makes it act larger and moves the alignment. Assembled and inspected in Tullahoma, Tennessee.

Is the PowerBass XL-1240T included with this enclosure?

No. This listing is for the enclosure only. Bring your own PowerBass XL-1240T. The cutout and cabinet height are cut direct fit for this driver. We do not stock PowerBass drivers.

Same series, same size

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